PARENT SESSION
Oral Session #80: Plant Ecology .
Presiding: G. Platenkamp
Thursday, August 8. 9:00 AM to 11:30 AM. Grand Ballroom West, Radisson.
Relative growth rates of three dominant semi-arid plant species: Direct and indirect effects of precipitation and potential evapotranspiration.
RESTREPO, CARLA*,1, POCKMAN, WILLIAM2, MILNE, BRUCE2, MARTENS, SCOTT3, ALLEN, ANDREW2, TYLER, ANA2, 1 University of Puerto Rico-RP, San Juan, PR, Puerto Rico2 University of New Mexico, Albuquerque, NM3 University of California-Davis, Davis, CA
ABSTRACT- The evolution of semi-arid landscapes strongly influences the distribution of resources and therefore large-scale patterns of vegetation. First, we explore the hypothesis that variation in the distribution of precipitation and potential evapotranspiration associated with complex terrain affects relative growth rates of the tree Juniperus monosperma, the shrub Larrea tridentata, and the grass Bouteloua spp. Second, we explore the hypothesis that variation in soil moisture affects relative growth rates of the above species but contingent on species combination. At the Sevilleta Wildlife Refuge, NM, we estimated plant growth rates as changes in biomass of a sample of twigs over a 2 yr period; we used a combination of field measurements and twig and grass allometries to calculate biomass. To test the first hypothesis we chose five sites representing a gradient in precipitation (PPT) and potential evapotranspiration (PET) and at each site followed 20 individuals of each species. To test the second hypothesis we established a large-scale experiment in which we added and eliminated water to several species combinations. Our results indicate that (1) PPT and not PET explains the observed variation in relative growth rates, (2) maximum relative growth rates for the three species occur at different levels of PPT, and (3) relative growth rates of Juniperus and Larrea are strongly influenced by soil moisture but for Larrea this is largely dependent on species combination.
KEY WORDS: arid landscapes, resources, plant, growth